1. Field of the Invention
The present invention relates to anaerobically curable compositions demonstrating resistance to elevated temperature conditions.
2. Brief Description of Related Technology
Anaerobic adhesive compositions generally are well-known. See e.g., R. D. Rich, “Anaerobic Adhesives” in Handbook of Adhesive Technology, 29, 467-79, A. Pizzi and K. L. Mittal, eds., Marcel Dekker, Inc., New York (1994), and references cited therein. Their uses are legion and new applications continue to be developed.
Conventional anaerobic adhesives ordinarily include a free-radically polymerizable acrylate ester monomer, together with a peroxy initiator and an inhibitor component. Oftentimes, such anaerobic adhesive compositions also contain accelerator components to increase the speed with which the composition cures.
Many adhesives particularly anaerobic adhesives, have been rendered resistant to degradation at elevated temperatures by the inclusion of certain additives. For instance, U.S. Pat. No. 3,988,299 (Malofsky) refers to a heat curable composition having improved thermal properties, which includes certain acrylate monomers and maleimide compounds.
L. J. Baccei and B. M. Malofsky, “Anaerobic Adhesives Containing Maleimides Having Improved Thermal Resistance” in Adhesive Chemicals, 589-601, L-H, Lee, ed., Plenum Publishing Corp. (1984) report the use of maleimides—specifically, N-phenyl maleimide, m-phenylene dimaleimide and a reaction product of methylene dianiline and methylene dianiline bismaleimide—to increase the thermal resistance of anaerobic adhesives which are fully cured at temperatures of at least 150° C.
While the addition to anaerobic adhesive compositions of such maleimide compounds to render them resistant to thermal degradation provides reaction products with acceptable performance, it would be desirable to find alternative compounds to include in such formulations.
Henkel Corporation in the past designed certain anaerobic adhesive compositions with enhanced resistance to thermal degradation. For instance, U.S. Pat. No. 6,342,545 (Klemarczyk) discloses and claims a radical curable composition, radical cured reaction products of which demonstrate improved adhesion and resistance to thermal degradation at elevated temperatures. The composition, which may cure under anaerobic conditions, includes (a) a (meth)acrylate component; (b) an effective amount of latent imidazole as a thermal resistance conferring agent; and (c) a radical cure-inducing composition, such as an anaerobic cure-inducing composition. The latent imidazole is an adduct obtained by a reacting a compound having an active hydrogen together with a tertiary amino group, an epoxy compound and a carboxcylic acid anhydride. And the thermal resistance-conferring agent is selected from methyl imidizole, benzoyl imidizole, benzoyl methylimidizole, phthaloyl diimidizole and combinations thereof.
U.S. Pat. No. 6,150,479 (Klemarczyk) also discloses and claims a radical curable composition, radical cured reaction products of which demonstrate improved adhesion and resistance to thermal degradation at elevated temperatures. The composition, which may cure under anaerobic conditions, includes (a) a (meth)acrylate component; (b) a coreactant component of certain structures, examples of which include epoxidized citronellyl acrylate; epoxidized citronellyl methacrylate; cyclohexenyl methanol acrylate; cyclohexenyl methanol methacrylate; epoxidized cyclohexenyl methanol methacrylate; dihydrodicyclopentadienyl acrylate; epoxidized dihydrodicyclopentadienyl acrylate; dihydrodicylopentadienyl methacrylate; epoxidized dihydrodicylopentadienyl methacrylate; epoxidized 2-propenoic acid, 2-[(3a,3,4,5,6,7,7a-hexahydro-4,7-methano-1H-indenyl)oxy]ethyl ester; epoxidized 2-propenoic acid, 2-methyl-, 2-[(3a,3,4,5,6,7,7a-hexahydro-4,7-methano-1H-indenyl)oxy]ethyl ester and combinations thereof; and (c) a radical cure-inducing composition, such as an anaerobic cure-inducing composition. Here, the presence of the coreactant in the composition provides radical cured reaction products thereof with improved adhesion and resistance to thermal degradation. The compositions may also include a thermal resistance-conferring agent, such as one selected from imidizole derivatives (such as benzoyl imidizole, methyl imidizole, benzoyl methylimidizole, phthaloyl diimidizole and combinations thereof), latent imidizoles, and an adduct obtained by reacting a compound having an active hydrogen together with a tertiary amino group in the molecule, an epoxy compound and a carboxylic acid anhydride.
Henkel also has sold and continues to sell a product called PST with boric acid (Item No. 190901), which has among other components about 1-5% of boric acid.
Despite the state of the art, there is an on-going search for additives to improve the thermal performance of reaction products of radical-curable adhesives, such as anaerobically curable ones.